1. Field of the Invention
The present invention relates to a data transmitting and receiving apparatus, particularly to an apparatus that transmits data to and receives data from a memory included in a sensor, which stores calibration data and the like.
2. Description of the Related Art
In related art, what is called a TEDS (Transducer Electronic Data Sheet) has been proposed in which a memory is included in a sensor and data on a manufacturer, kind, type, serial number, calibration value, calibration date and time, and the like of the sensor are stored in the memory to be read and written in accordance with the necessity, and TEDS is standardized as IEEE1451.4. TEDS has a simplified configuration in which a single signal line is shared by a signal line from the sensor and a data line that performs read/write of data on the memory. Since a signal detected by the sensor is typically output from the sensor as a voltage signal having a positive value, a binary signal having a negative value is used as digital data output from the memory in order to prevent a collision with the above signal. The sensor signal may be driven by +5V and the digital data of the memory may be driven by −5V. Hereinafter, a system including a sensor provided with a memory and a data transmitting and receiving apparatus to which a signal detected by the sensor and data from the memory are input and which supplies various kinds of commands or the data to be write-in to the memory, is called a TEDS system in this description.
FIG. 1 is a block diagram showing a configuration of the TEDS system. A sensor 10 and a data transmitting and receiving apparatus 18 are connected by a single signal line 1. An amplifier 12, a sensor element 14 and a TEDS memory 16 are provided in the sensor 10. The amplifier 12 and the sensor element 14 are connected in series to the signal line 1 through a diode and are further connected to a GND terminal on the apparatus 18 side. Further, a negative side terminal of the TEDS memory 16 is connected to the signal line 1 through the diode, and a positive side terminal of the TEDS memory 16 is connected to a GND terminal on the apparatus 18 side. A switch 20 that switches between an analogue terminal (ANALOG) and digital terminal (DIGITAL), a constant electric-current source 22 connected to a positive power supply and a negative power supply 24, are provided in the data transmitting and receiving apparatus 18. The switch 20 is switched to the analogue terminal side when the sensor element 14 is driven, and the switch 20 is switched to the digital terminal side when the TEDS memory 16 is driven.
FIG. 2 shows a configuration in the case where the switch 20 is switched to the analogue terminal side. Since the sensor 10 is connected to the constant electric-current power source 22 of a positive voltage (+5V for example) in the apparatus 18, the sensor element 14 is driven by a constant electric-current through the diode on the upper side in the figure. The sensor element 14 is, for example, a three-axis acceleration sensor element of a piezoresistance type, and an analogue sensor output (voltage signal) corresponding to the acceleration is output from an analogue signal output terminal on the apparatus 18 side. After being converted into a digital signal in an A/D converter, the analogue sensor output is stored in the memory of the apparatus 18, for example. The apparatus 18 functions as a data recorder for the sensor 10.
FIG. 3 shows a configuration in the case where the switch 20 is switched to the digital terminal side. Since the sensor 10 is connected to the power source 24 of a negative voltage (−5V for example) in the apparatus 18, logic power is supplied to the TEDS memory 16 through the diode on the lower side in the figure and the transmitting and receiving of data is executed between the TEDS memory 16 and a digital data I/O in the apparatus 18. Specifically, a data driver of the apparatus 18, which has input and output terminals, is connected to the digital data I/O and when a calibration value and the like of the sensor which are stored in the TEDS memory 16 are read out, a read command is transmitted from the data driver and digital data transmitted from the TEDS memory 16 is received by the data driver in accordance with the read command. Further, when data is newly written into the TEDS memory 16 (or the data is renewed), write data is supplied from the data driver to the TEDS memory 16 following a write command. However, because the TEDS memory 16 is based on the negative voltage (−5V) and typically the data driver is driven by the positive voltage, the transmission and reception of data with respect to the TEDS memory 16 becomes a inverted logic and a logic inversion circuit is needed for transmitting and receiving the data between the data driver and the TEDS memory 16.
FIG. 4 shows an example of the logic inversion circuit provided in the apparatus 18, in which a transformer 26 is used as an inversion element, for example. Data transmitted from the TEDS memory 16 to the apparatus 18 (an input signal when seen from the apparatus 18) is a rectangular pulse signal that has the reference −5V with 0V as the peak value. The data values “0” and “1” are expressed with a pulse width, respectively and the data value “1” is expressed with a short pulse width and the data value “0” is expressed with a long pulse width. One terminal on the output side of the transformer 26 is connected to the GND and the inverted signal is obtained from the other terminal. The output signal is the rectangular pulse signal that has the reference 0V with 5V as the peak value.
An inversion circuit using a transformer is disclosed in the following Patent document 1.
Patent document 1: PCT Publication No. WO 02/052861 A2.